Electronically scanning antennas have a radiating array which is formed by a matrix of radiating sources disposed on a plane surface, the sources being horns or dipoles, for example, which are fed with primary waves. The primary waves differ in phase in such a way that the wave which is radiated into space is a plane wave whose planes of equal phase lie in a selected direction. In such antennas, the scanning of the beam is effected by varying the phase difference between the radiating sources in the array under electrical control in such a way as to alter the direction of the plane of the emergent wave. The radiating elements at the surface are associated with respective wave guides for the signal and the wave guides incorporate members termed phase shifters. The phase shifters used in electronically scanning antennas may, for example, be switching ferrites or switching diodes. Phase shifters equipped with PIN-type diodes, used in the context of the present invention, are extremely reliable and are capable at operating at very high frequencies. The function of the diode-equipped phase shifters is to produce phase increments at microwave frequencies and the accuracy with which these increments are produced is related to that of the current passing through the diodes.
In the prior art, the necessary accuracy in the conduction current is obtained by using a stabilized low-voltage power supply and external components such as a network of load resistors. However, the stabilized power supply delivers a regulated voltage which is common to all the phase-shifting diodes and, this being the case, the relatively great distance between the unregulated energy source and the stabilized power supply causes disturbances which give rise to uncontrolled phase shifts.
In addition, the level of the combined control current for the group of phase-shifting diodes, of which, to give an example, there may be from 1000 to 10,000 in an electronically scanning antenna, is such as to require the use of a high-power low-voltage power supply which is both bulky and expensive.
Because of this, it is necessary to use heavy cables to distribute the regulated voltage. Since the voltages used are low and the currents may reach several hundreds of amperes, the voltage drop in the conductors between the various phase shifters gives rise to an appreciable variation in the regulated voltage supplied to the load which exceeds the 7% limit normally tolerated. In the radiation diagram, this discrepancy gives rise to secondary lobes whose mean level is excessively high.
In addition, the large temperature variations in the phase-shifting arrangement, which are due to energy dissipation, detract from the regulating performance.